
class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if(p == root || q == root) {
            return root;
        }
        if(root == null) {
            return null;
        }
        TreeNode l = lowestCommonAncestor(root.left,p,q);
        TreeNode r = lowestCommonAncestor(root.right,p,q);
        if(l != null && r != null) {
            return root;
        } else if(l != null) {
            return l;
        } else if(r != null) {
            return r;
        }
        return null;
    }
}